Clostridia-Associated Enterocolitis in Foals

Clostridia-associated enterocolitis (inflammation of the small intestine and colon) affects both humans and horses, young and old alike. According to Nathan Slovis, DVM, Dipl. ACVIM, of Hagyard-Davidson-McGee (HDM) Associates veterinary clinic in Lexington, Ky., more than 20% of foals within the first six months of age will have an infectious diarrhea. He said that several authors have reported associations between enteritis (inflammation of the intestine) and diarrhea in foals and the various clostridial organisms. Slovis discussed the pathogenesis, clinical signs, diagnosis, and treatment of enterocolitis associated with Clostridium difficile and Clostridium perfringens at the HDM Bluegrass Equine Reproduction Symposium on Oct. 24, 2002.

Clostridium difficileHis presentation began with a discussion on Clostridium difficile, a gram-positive anaerobic bacillus that is believed to be responsible for almost all cases of pseudomembranous colitis (an acute inflammation of the colon) and 20% of antibiotic-induced colitis in humans. In antibiotic-induced colitis, the C. difficile disrupts the normal flora in the colon. C. difficile is able to form heat-resistant spores in the environment that can persist for years. These spores convert to a vegetative form in the colon. When established, disease-causing strains will produce toxins--toxin A, toxin B, and a recently found third toxin.

Many cases of human infection come from C. difficile in hospitals, and colonization in newborns can be common, but newborns are usually asymptomatic. C. difficile has been implicated in an outbreak of colitis among horses at veterinary teaching hospitals, said Slovis. Slovis reported that a small percentage of foals (0-3%) are asymptomatic carriers, similar to adult humans. From less than 1% to 15 percent of adult horses are asymptomatic, and these numbers are similar to statistics for humans. Slovis cautioned that sometimes a foal might be harboring C. difficile despite never having received antibiotics. He cited one study in which 10 out of 25 horses which developed acute colitis had C. difficile.

Foals with C. difficile might have symptoms ranging from a low-grade diarrhea to violent colitis with decreased motility of the intestines, anorexia, dehydration, rapid breathing, fever, lowered blood pH, lowered amounts of protein and sodium in the blood, and lowered circulating plasma in the body. Diagnosis is confirmed by isolating C. difficile from feces. Because about 25% of C. difficile do not cause disease (they do not have the necessary toxins), a cytotoxin assay, with a sensitivity of 94-100%, can be performed to determine if the organism is pathogenic. This test can be expensive. Therefore, it is not used often, Slovis said. He mentioned that there are now two new enzyme immunoassays that can be used to detect either the toxins or the antigens. (Slovis cautioned not to use sytrofoam when submitting a fecal sample since this can bind the toxins.) In addition, a polymerase-chain reaction (PCR) test can be done; however, like the cytotoxin assay, these are expensive as well as time consuming.

Slovis first begins treatment by discontinuing any antibiotics the horse might be on, if this is a viable option. His first choice for a drug is oral metronidazole since the response rate in humans is 98%. When fighting metronidazole-resistant strains, he recommended vancomycin. He said that it was important to continue the treatment for five days past the end of the diarrhea due to a risk of relapse. In addition, Slovis will use fluid therapy to correct the pH imbalance, and he recommends that stalls be cleaned with water and detergent. Slovis said that “elbow grease” must be used because it is the mechanical aspect of cleaning that can remove spores from the stall. The spores are highly resistant to all chemicals, and therefore persist in the environment. So scrubbing them off of the walls and floors and rinsing them out of the stalls is necessary.

Clostridium perfringensThis bacterium is easily distributed as vegetative spores in the soil and found in fecal matter, and it is commonly found in the gastrointestinal tract of many warm-blooded species, said Slovis. There are five major types (A, B, C, D, and E) and five toxins (alpha, beta, epsilon, iota, Beta 2-toxin) associated with C. perfringens. Isolates might also have a gene called C. perfringens enterotoxin (CPE), which in one study was found in isolates from 16% of adult horse feces and 10% of the horses in the study with colic, cited Slovis. He said that CPE has been detected in the feces of 7-33% of adult horses with diarrhea and 28% of foals with diarrhea.

Although how C. perfringens causes disease is not entirely known, it is believed that something causes an alteration in the flora in the digestive tract, which allows overgrowth of this clostridia. Possible causes for the alteration can include diet changes, antibiotic use, or infection. Disease associated with C. perfringens is usually found in foals less than five days of age with a history of being dull, colicky, and having diarrhea for less than 24 hours. Sick foals usually are dehydrated with severe colitis, and they could develop decreased intestinal motility. Blood pH becomes more acidic, blood glucose is lower, and there is an abnormal decrease in white blood cells. Foals which suffer from peritonitis (infection of the lining of the abdomen) have a grave prognosis in which euthanasia is usually recommended, said Slovis.

When making a diagnosis, Slovis said that culture alone is questionable and presumptive. He cited one report in which the organism was cultured from 90% of foals by three days of age. He said that the toxins and organisms must be identified and isolated. This can be done with an Elisa test to detect CPE or with a PCR test.

Any disease caused by C. perfringens should be considered a medical emergency, he said. Veterinarians will treat associated abdominal pain, septic shock, clostridial infection, toxin production, and maintain nutrition of the horse. Again, Slovis prefers to use metronidazole, and he will use neostigmine to treat any severe gas distention of the colon. For the first 48-72 hours of life, C. perfringens type C and D toxoid can be given to neonates, he said. However results have varied. He also said that he has given hyperimmunized plasma with some success.

Proper management of foaling mares can help reduce the risk of infection with C. perfringens in their foals. Slovis recommended cleaning the stall well before the birth. The mare’s udder, perineal region, and hind limb region should be cleaned before and after birth. He said that some people foal mares outside to reduce the risk of disease. In addition, starting mares on metronidazole after foaling as a preventive measure might be an option. Mares should be vaccinated with the type C (or types C and D) toxoid four to six weeks before foaling and again two to three weeks before foaling.

About the Author

Sarah Evers Conrad has a bachelor’s of arts in journalism and equine science from Western Kentucky University. As a lifelong horse lover and equestrian, Conrad started her career at The Horse: Your Guide to Equine Health Care magazine. She has also worked for the United States Equestrian Federation as the managing editor of Equestrian magazine and director of e-communications and served as content manager/travel writer for a Caribbean travel agency. When she isn’t freelancing, Conrad spends her free time enjoying her family, reading, practicing photography, traveling, crocheting, and being around animals in her Lexington, Kentucky, home.

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